Thank you both very much for that feedback.
The untreated brick end wall is the back wall of the live/tracking area, and at the moment its doesn't cause a noticeable problem except during mixdown and at relatively high levels. I think that wall will need quite a lot of treatment as it has a large surface area.
So far, I have tried to keep the mix position as symmetrical as possible, but I can foresee the small plastered brick wall directly behind and to the left the mix position causing some problems as it makes the mix position slightly asymmetrical. Ideally It would be nice to take out the wall completely as it doesn't offer much isolation from live instruments, but it is a supporting wall crucial to the stability of the house...
It looks like I have some reading to do!
Thanks again guys! Any more comments suggestions are welcome.
